New answers tagged

1

Clarifications There is a difference between a solar flare and a the phenomena that cause things like the 1989 Quebec blackout and/or the 1970s New York blackout (I think it was 1972 but do not recall off hand). The latter phenomena are called coronal mass ejections (CMEs) because they actually involve large amounts (i.e., upwards of billions of tons) of ...


1

Just to confirm that CuriousOne is correct as regards direct radiation damage to your body. From Solar Flares Solar flares are gigantic explosions associated with sunspots, caused by the sudden release of energy from “twists” in the sun’s magnetic field. They are intense bursts of radiation that can last for anywhere from minutes to hours. Solar flares ...


1

The motion of a charged particle in a magnetic field is the manifestation of the fundamental relationship between magnetism and electrostatic effects. Exactly why the fundamental forces are the way they are is still beyond modern day physics which is why it is hard to give a satisfactory answer to the first part of your question. It just has to be accepted ...


0

Normalization Factor Let us define a generalized Gaussian probability density function (PDF) as: $$ f_{s}\left( x \right) = A_{o} \ e^{^{\displaystyle - \frac{ (x - x_{o})^{2} }{ 2 \sigma^{2} } }} \tag{0} $$ where $A_{o}$ is the normalization constant, $x$ is the argument, and $s$ denotes the set of distributions (e.g., particle species), $x_{o}$ is the ...


1

Are there more positive than negative charges released? In general no, and this statement by itself would imply you were asking about whether the sun charges up, not about current. I wrote a detailed answer at http://physics.stackexchange.com/a/253491/59023 that explains why stars remain mostly neutral and that most observations [e.g., Bale et al., ...


0

Why is it that an oscillating electric field transfers energy less efficiently to ions than to electrons? This is not generally true. There are multiple cases where an oscillating electromagnetic field transfers energy/momentum much more efficiently to ions than electrons (e.g., Alfvén waves do not care about electrons in many situations). In lab ...


-1

The sun is a ball of plasma. It is essentially a group of electrons and nuclei whizzing around. These electrons and nuclei correspond to no net charge. The get flung out into space still in the form of plasma. There is still no net charge. The individual particles have charge but no net charge.


3

The mass of the electron is thousands of times less than that of the ions - about 1,800 times lighter than a proton. The motions move the entire ion core, so inertia tends to resist the change of motion much more than is possible for an electron. For example, see Improved Two-Temperature Model and Its Application in Ultrashort Laser Heating of Metal Films. ...


-1

Personally think the donut geometry is flawed. An egg shaped geometry would be better suited, as energy naturally wants to vortex (convection) with the differences in temperature. HOT down a central vortex and cool on the outer edge. Hot expanding to cool and cool contracting to heat. Plus with no centre point of focus in the donut, it does not mimic the ...


0

I think I've figured out why. It's simply because the critical density $n_{crit}$ is a function of $\omega$. The critical density of the plasma is that which is required for the EM wave frequency to equal the plasma frequency $\omega_p$, so is dependent on the frequency of the radiation. So $$\omega=ck\left(1-\frac{n_e}{n_{crit}(\omega)}\right)^{-1/2}$$ ...


0

When the phase velocity is a constant (with respect to wavelength), the group velocity will indeed be equal to it, as you yourself have shown. What you've got wrong here is the assumption for this case that the product of the phase velocity and group velocity equal the square of the speed of light, which can be true in other cases but not for plasma ...


3

You may have things a bit mixed up. Plasma is not something that plays a role in fusion as if it were a tool or an instrument for its achievement. It is instead the only possible medium where nuclear fusion can occur: very basically, high enough temperature for protons to overcome the Coulomb repulsion, and high enough density for increased chances of ...


1

At the temperatures required for fusion reactions, matter can only exist in the plasma state. That's rather inconvenient for designers of fusion reactors, since plasma is hard to control and contain. And that's why the claims about cold-fusion were so appealing. Cold fusion promised to provide fusion power without the hassle of dealing with high temperature ...


4

How can particles that exist where quantum mechanics "reigns supreme" be modeled successfully as classical particles? If the model is useful, it gets wide popularity and sticks in physics irrespective of which framework - classical, probabilistic or quantum - it seems closest to. The idea that the quantum theory is some kind of ultimate theory of ...


2

The Drude model (1900) is based on statistical mechanics plus Maxwell's electrodynamics as updated by Lorentz to include the electron and atoms. It gives good results for some processes, such as conductivity/resistance of metals, but is way off on others, such heat capacity, and totally ignores important features such as band structure. The semi-classical ...


2

The primary difference is that the electrons in metallic hydrogen are nearly completely degenerate. Degenerate electrons cannot be dissipatively scattered and lead to the "metallic" characteristics of extremely high electrical and thermal conductivity. To first order, to produce metallic hydrogen you need to make sure that the electron kinetic energy at ...


2

In metallic hydrogen, the protons share an approximately fixed location relative to each other - energetically, a lattice is more favorable than an randomized state. Because of this, the substance is not a plasma - in a plasma, the positive and negative charges both flow freely. Metallic hydrogen only exists at very low temperatures, and very high ...


0

Current is the amount charge that goes through a particular cross section area per unit of time. It does not matter whether the charge density is uniform or not for this current to be non-zero; the only thing that prevails is whether or not the charges are flowing. Observable features that a current is passing comprise for instance Joule heating of the wire ...


8

Background Stars are composed of plasmas, which are an ionized gas that exhibit a collective behavior much like a fluid. There are two important aspects of plasmas to keep in mind. The first is that they act like very highly conductive metals in that the electrons can move very freely in order to cancel out any charge imbalance. The consequence is that ...


10

Overall, a star stays more or less neutral. This is true for all stellar objects beside black holes. I am using a simple calculation that can be found in a footnote of https://arxiv.org/abs/1001.3294 on p. 11 chap. 2. Suppose the star has an overall charge of Z times the elementary charge, $Ze$, and we consider the Coulomb repulsion of a test particle, say ...


1

In the case of the second order acceleration, two clouds are approaching, therefore the energy the charged particle gains comes from the energy of the clouds. In the case of the first order acceleration, the charged particle gains energy as it moves repeatedly through the shock front. The region before the shock front (upstream) moves at higher speed than ...


4

Note You should clarify your statement from "...a charged particle cannot gain energy from a magnetic field..." to "...a charged particle cannot gain energy from a static magnetic field..." There is nothing wrong with energy transfer from time-varying magnetic fields. Background If the spatial gradient in the magnetic field is slow enough such that the ...



Top 50 recent answers are included